Radioactive iodine and cesium from the Fukushima No. 1 nuclear power plant likely spread across a wide area encompassing Tohoku, Kanto and parts of Chubu, according to a simulation by the National Institute for Environmental Studies.
Radioactive iodine and cesium from the Fukushima No. 1 nuclear power plant likely spread across a wide area encompassing Tohoku, Kanto and parts of Chubu, according to a simulation by the National Institute for Environmental Studies.
The results of the study are expected to provide a basis for information used in decontamination efforts and other quake-related projects.
"The simulation data does not necessarily reflect actual measurements," said Toshimasa Ohara, head of the institute's Center for Regional Environmental Research. "We want the data to be used as reference figures and indicators of where to measure radiation levels, especially in areas where the results indicate high levels."
Taking into account weather conditions, such as wind directions and rainfalls, Ohara estimated the amount of nuclear substances from the plant that had fallen on the ground and in nearby waters from March 11, when the Great East Japan Earthquake struck, until March 29, the date the radiation fallout was believed to have mostly eased off.
The results indicate the possibility that 13 percent of leaked iodine-131 and 22 percent of released cesium-137 fell on soil in 15 prefectures. Cesium-137 was estimated at high levels in spots scattered across a broad area, including Shizuoka, Nagano and Niigata prefectures.
In early May, the science ministry published the results of the System for Prediction of Environmental Emergency Dose Information (SPEEDI) to estimate the spread of radiation from the plant.
Many of SPEEDI's radiation monitoring locations recorded values close to the ones estimated by Ohara's simulation project. But the SPEEDI measurements were largely limited to an area close to the plant.
After radioactive cesium was detected in tea leaves in Shizuoka, Kanagawa and other prefectures, calls from the public intensified for assessments covering a much wider area.
The simulation map can be found on the National Institute for Environmental Studies' website in Japanese at (http://bit.ly/qImVbY).